Yes the HD-6450 at least has H264 video support. For gaming it's not much better than the 6150se. This is mostly because the 6150se cheats by using dx9.0c shaders and the hd-6450 gets crippled by dx11 graphics.
on ebay there is shipping and some other fees too so it's not just $17. I will say it's $30.
Also you need to fix vista. Google the speed tweeks people do. It worked for my computer. It boots up about 3x faster.
With amd stick with at least 320 shaders with at least 600 shaders being ideal. With the 9800gt it's 128 shaders are ok, but with the Geforce 260 and newer stick with 260 shaders and more.
Look locally for a used card, try and get one with the molex to pcie power connectors that it needs included. (They should be about $10 each so at that point a new power supply like the antec or corsair or ocz budget ones would be a better choice.)
If you luck out and find a HD-5750, 5770, 6750, 6770, 6790, 6850, 7750, 7770, 7790, 7850, amd 260,270,270x,360,370. Geforce 440,540,550,640, 650, 730, 740, 750, 940, 950. Those cards should run without turning the speeds down as they are 150watts and under.
The old HD-3850, 3870, 4650, 4670, 5650, 5670, 6650, 6670 and geforce 8600gt, 9600gt would also be ok but not the fastest of the bunch.
You want to find a card that is both fast but is not high wattage.
A popular card in the past was the Geforce 9800GT , you might find one for $20. Those cards are dx-9.0c but are fast and should work well, they also don't use lots of power. DO NOT GET THE 8800GT OR 8800GTX OR 9800GTX OR 250 THEY USE TOO MUCH POWER.
The smaller and lower wattage cards are sought after and people tend to hang onto them, so it is likely a larger and faster card will be cheaper.
THESE CARDS ARE NOT IDEAL, BUT IF YOU SEE ONE FOR $20 OR SO, UNDERCLOCKING COULD GIVE YOU A DECENT BUDGET CARD.
The Geforce 260,275,280,285,450,460,550,560 and HD-4870,4850, 5830,6870, could also be cheap but will need to be underclocked and maybe undervolted to work.
Some cards like the Geforce 470, 480, 570, 580, HD-6950, 6970, 5950, 5970 are too large to work and would need extreme things like a bios mod to turn down that much. I would not get something that is too large and too many watts.
Look up the gaming charts on tom's for wattages and fps in games.